The construction and operation of rotating drum image scanning equipment is well known in the art of electronic image reproduction equipment. Basically, the image which is placed on the drum is scanned in a spiral with a small pitch which is set according to the required lines per inch resolution, so that during scanning the light beam moves slowly from the left side of the drum to the right side. Since the scanning line pattern is essentially perpendicular to the drum revolution axis, the angle of the image provided during scanning has a one-to-one relationship with the angle with which the material to be scanned is placed on the drum.
If, during the set-up procedure for this type of equipment, the material to be scanned is placed on the drum incorrectly, such as for example, where the edge of an original print is not properly aligned with the direction of drum revolution, the resulting image reproduction will be tilted. This misalignment is likely to be evident especially where several pictures are to be combined on one page, and normally is corrected by repositioning and re-scanning the image, after which the whole process may have to be repeated yet again if another error is found.
It would therefore be desirable to simplify the operation of drum scanning equipment and allow correction of misaligned pictures.
In addition, the required enlargement and rotation angle for a picture must be measured before the picture is put on the drum. This is a time consuming process which usually requires special equipment such as an enlarging machine.
It would therefore be desirable to measure the rotation angle in a fast interactive process while the picture is on the drum so that it can be corrected automatically during scanning.